This project involves both clinical studies of humans infected with the intestinal nematode, Strongyloides stercoralis, and analysis of parasite antigens and immunologic responses to them. The parasite is of particular interest because of its unusual biologic properties and the fact that it can produce serious, even fatal, disease in certain immunosuppressive states. Several approaches to affinity purification of the parasite larval protease were attempted. One method was conventional use of monoclonal antibody, and the other involved conjugating one of the zinc metallo-protease inhibitors to sepharose and elution of the protease from such a substrate. The evidence for purification of the protease by either method remains equivocal. A continuing problem in interpretation of results is the variability in molecular size of the protease under different physico chemical conditions. Clinical and serologic studies have continued for evidence of strongyloidiasis in different population groups with high prevalence of infection with the retroviruses, HIV and HTLV-1. The possibility that serum IgE response may be an important factor in controlling strongyloides infection is also being examined. The parasite did not appear to be important as an opportunistic infection in a limited number of AIDS patients in Zaire, and their IgE responses were not impaired. In contrast, mean serum IgE levels were reduced in certain groups of patients positive for HTLV-1 in Jamaica.